U.S. patent application number 11/724248 was filed with the patent office on 2007-07-12 for processing network communication control messages.
This patent application is currently assigned to BRITISH TELECOMMUNICATIONS public limited company. Invention is credited to Shaun S. Baker, Caroline M.O. Beauchamps, Philip M. Clarke, Paul J. Felton, Alan W. O'Neill.
Application Number | 20070162613 11/724248 |
Document ID | / |
Family ID | 8172821 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070162613 |
Kind Code |
A1 |
O'Neill; Alan W. ; et
al. |
July 12, 2007 |
Processing network communication control messages
Abstract
Control messages constructed in accordance with a first
communications protocol for use in a communications network each
include a first address identifier having a format defined by the
first protocol. The control message is processed to derive a second
address identifier having a format defined by a second
communications protocol. The control message is re-formatted for
transmission, in accordance with the second protocol, to a network
system associated with the second address identifier.
Inventors: |
O'Neill; Alan W.; (Ipswich,
GB) ; Clarke; Philip M.; (Ipswich, GB) ;
Felton; Paul J.; (Ipswich, GB) ; Beauchamps; Caroline
M.O.; (Hertfordshire, GB) ; Baker; Shaun S.;
(Zurich, CH) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
BRITISH TELECOMMUNICATIONS public
limited company
London
GB
|
Family ID: |
8172821 |
Appl. No.: |
11/724248 |
Filed: |
March 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10220498 |
Aug 30, 2002 |
|
|
|
PCT/GB01/01343 |
Mar 26, 2001 |
|
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11724248 |
Mar 15, 2007 |
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Current U.S.
Class: |
709/238 |
Current CPC
Class: |
H04L 67/2804 20130101;
H04L 69/08 20130101; H04L 61/00 20130101; H04L 29/12009 20130101;
H04L 69/40 20130101; H04L 69/169 20130101; H04L 69/16 20130101;
H04L 69/327 20130101; H04L 67/2814 20130101 |
Class at
Publication: |
709/238 |
International
Class: |
G06F 15/173 20060101
G06F015/173 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2000 |
EP |
00302424.7 |
Claims
1. A method for processing messages in a unified packet network
capable of processing and delivering packet messages using first
and second destination address formats, said method comprising:
transmitting a message into a packet network having a first
destination address format encapsulating information sufficient to
derive a second address format for the same destination; if said
first address format is determined not to be deliverable in said
network, then deriving said second address format from said
encapsulated information and re-transmitting said message into said
network using said second address format for said destination.
2. A method as in claim 1 wherein said first address format is in
accordance with SIP and said second address format is in accordance
with SMTP.
3. A method as in claim 1 wherein if said first address format is
determined not to be deliverable then an error message is also
generated and sent to the intended message recipient using said
derived second address format.
Description
CROSS REFERENCE TO RELA TED APPLICA TIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/220,498 filed Aug. 30, 2002 which was the
national phase of PCT/GB 01/01343 filed Mar. 26, 2001 and which
claimed priority from EP application 00302424.7 filed Mar. 24,
2000, the disclosure of which priority applications is incorporated
herein by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] This invention relates to processing control messages for
use in communications network, and in particular to a method, data
processing system and software application program for processing
control messages constructed in accordance with a communications
control protocol. The invention is particularly, but not
exclusively, directed to text-based application-layer communication
control protocols.
[0004] 2. Related Art
[0005] The Session Initiation Protocol (SIP) is an
application-layer control protocol for creating, modifying and
terminating sessions having one or more participants. These
sessions include Internet multimedia conferences, Internet
telephone calls and multimedia distribution. Members in a session
can communicate via multicast or via a mesh of unicast relations,
or a combination of these. SIP supports session descriptions that
allow participants to agree on a set of compatible media types. It
also supports user mobility by proxying and redirecting requests to
the user's current location. SIP is not tied to any particular
conference control protocol. There is widespread interest in the
protocol, especially for telephony-related applications. SIP was
proposed by the Internet Engineering Task Force (IETF) group and is
now a proposed standard published as RFC 2543.
[0006] The entities used in SIP are user agents, proxy servers,
redirect servers and location servers. A SIP user agent is an
end-system that allows a user to participate in a session. A SIP
user agent contains both a user agent client and a user agent
server. A user agent client is used to initiate a session and a
user agent server is used to respond to request from a user agent
client. A user is addressed using an email-like address identifier
"user@host", where "user" is a user name or phone number and "host"
is a domain name or numerical Internet Protocol (IP) address. SIP
defines a number of request types, in particular INVITE, ACK, BYE,
OPTIONS, CANCEL, and REGISTER. Responses to SIP messages indicate
success or failure, distinguished by status codes, 1xx (100 to 199)
for progress updates, 2xx for success, 3xx for redirection, and
higher numbers for failure. Each new SIP transaction has a unique
call identifier (call ID), which identifies the session. If the
session needs to be modified, e.g. for adding another media, the
same call identifier is used as in the initial request, in order to
indicate that this is a modification of an existing session.
[0007] The SIP user agent has two basic functions: listening for
incoming SIP messages, and sending SIP messages upon user actions
or incoming messages. The SIP user agent typically also starts
appropriate applications according to the session that has been
established. The SIP proxy server relays SIP messages, so that it
is possible to use a domain name to find a user, for example using
the Domain Name System (DNS) rather than knowing the IP address or
name of the host. A SIP proxy can thereby also be used to hide the
location of the user. A redirect server returns the location of the
host rather than relaying the SIP message. Both redirect and proxy
servers accept registrations from users, in which the current
location of the user is given. The user's location can be stored at
a dedicated location server.
[0008] SIP is typically implemented by transmitting Internet
Protocol (IP) packets. SIP is independent of the packet layer and
only requires an unreliable datagram service, as it provides its
own reliability mechanism. While SIP typically is used over UDP or
TCP, it could be used over frame relay, ATM AAL5 or X.25.
[0009] SIP is a text based protocol and is based to a certain
extent (in terms of syntax) on the HTTP protocol. A typical message
consists of a single request line, a number of header lines and a
message body.
[0010] The request line indicates the type of the messages, the
message destination and the SIP version it complies with. The
following is a typical example: INVITE sip:Richard@bt.com
SIP/2.0
[0011] A header line contains the name of the header type, followed
by a semicolon and the contents as these are defined for the
specific header. Consequently, each header type is used for a
specific purpose (either to indicate some parameters or to issue a
request). The following are typical examples: [0012] From:
sip:Richard@bt.com [0013] To: sip:Steve@bt.com [0014] Subject:
Official meeting
[0015] The message body may be of any content, although it usually
has contents formatted in accordance with the Session Description
Protocol (SDP).
[0016] SIP URL address identifiers such as sip:Richard@bt.com are
required for the exchange of SIP messages in a similar way that
e-mail URL address identifiers are required for the exchange of
electronic mail.
[0017] By using an e-mail type address it is possible to deliver a
SIP message to a SIP server that knows the location of the user or
user agent server the message is intended for. The IP address of
the SIP server having authority for the callee's address can be
readily determined by DNS. However, this approach requires users of
both SIP and e-mail services to be allocated different and
potentially confusing SIP and e-mail addresses. This exacerbates
the problem of address memory, address book maintenance and in
particular, address resolution using database queries. A further
problem associated with SIP is that as a newly implemented protocol
there is no delivery guarantee, that is to say delivery of a SIP
message addressed using a SIP URL may fail, for instance because
the intended recipient is not enabled to receive SIP messages.
BRIEF SUMMARY
[0018] According to an aspect of the present invention there is
provided a method for processing control messages constructed in
accordance with a first communications protocol for use in a
communications network, each control message including a first
address identifier having a format defined by said first protocol;
said method comprising the steps of: [0019] i) processing said
control message to derive a second address identifier from said
first identifier, said second identifier having a format defined by
a second communications protocol; and, [0020] ii) re-formatting
said control message for transmission, in accordance with said
second protocol, to a network system associated with said second
address identifier.
[0021] In this way, a control message constructed in accordance
with a first network protocol can be readily converted for
transmission over a second network protocol to a network system
having an network address identifier constructed in accordance with
the second protocol. The integration of new communications services
implemented over a new protocol can be improved with the above
method. For instance, a control messages constructed in accordance
with a newly implemented communications protocol can be readily
converted for transmission to a network address associated with a
communications service provided over a widely implemented protocol
where the address corresponds to an intended destination address
associated with a new communications service provided over the
newly implemented protocol. For instance, if a message is sent but
not delivered to a user or location identified by an address
identifier associated with a newly implemented protocol, the
address identifier can be resolved back to an address identifier
associated with a widely implemented protocol and the message sent
to the location associated with that resolved address by means of a
service available over the widely implemented communications
protocol. This may be necessary, for instance, if the network
system associated with the original address identifier is not
capable of receiving control messages constructed in accordance
with the newly implemented protocol. A further advantage of the
above method is that users can readily address messages etc, for
transmission over one communications protocol using an address
identifier associated with another communication protocol. The
ability to make use of the address space associated with a widely
implemented communications protocol is very important when say new
services are to be introduced using a new protocol. For example, a
user may address a message to another user using a new address
identifier derived from a known identifier regardless of whether
the user is aware of the recipient's address identifier for the
newly introduced protocol or whether the recipient has indeed been
allocated a new address identifier or is capable of receiving the
message over the new protocol. In the context of the present
invention it is to be understood that all or part of the control
message may be re-formatted for transmission over the second
protocol. For instance, the address identifier only may be
re-formatted and the remainder of the message discarded.
[0022] Preferably, a control message is processed in accordance
with steps i) and ii) in response to a detected delivery failure of
said control message to a network system associated with said first
address identifier. In this way if a control message fails to be
delivered using a communication service provided over one protocol,
say a newly implemented protocol, the message can be processed
according to the above method for delivery over another
communications protocol, for example a widely implemented
protocol.
[0023] Conveniently, said control message is processed in response
to said first address identifier being identified as an invalid
address identifier. In this way a control message having invalid
destination address identifier can be processed for transmission by
means of a service implemented over another protocol to a valid
network address recognised by that protocol.
[0024] In preferred embodiments, said control message is processed
in response to said network system associated with said first
address identifier failing to respond to said message. This allows
control messages to be processed for delivery by another
communications service when the intended destination network system
is unavailable or unwilling to receive control messages delivered
in accordance with one network protocol but available or willing to
accept messages delivered in accordance with another network
protocol.
[0025] Preferably, said method further comprises the step of
selecting a pre-determined error message for transmission to said
network device associated with said second address in accordance
with a respective failure mode associated with said detected
control message delivery failure. In this way a destination end
user or end system can be informed of a detected delivery
failure.
[0026] Conveniently, said method further comprises the step of
linking said control message to said pre-determined message for
transmission to said network device associated with said second
address identifier. In this way data contained in the control
message can be made available to the intended recipient in such a
way that pre-determined message templates can be used for message
construction.
[0027] In preferred embodiments, said pre-determined message
comprises executable code, or an network address identifier for
accessing executable code, wherein said code is capable of
processing said control message in accordance with said first
protocol. In this way end systems or users can readily access
software programs for receiving communications services provided
over a newly implemented protocol.
[0028] Preferably, said pre-determined message comprises a
pre-defined data structure for registering said first address
identifier with an address database associated with said first
protocol. In this way end systems or users can readily register an
address identifier for receiving communications services provided
over a newly implemented protocol.
[0029] Conveniently, said first address identifier comprises at
least one address component and said step of processing said
message comprises constructing said second address identifier to
include at least one component of said first address. In this way
address components can be common to both first and second address
identifiers.
[0030] In preferred embodiments, said second address identifier is
contained in said first address identifier and said method
comprises the step of parsing said control message to identify said
first address identifier and determine said second address
identifier from said first address identifier. This enables the
second address identifier to be readily derivable from the first
address identifier.
[0031] Preferably, said first protocol is an application layer
control protocol. This provides for the implementation of user
applications and new communications services.
[0032] Conveniently, said application layer control protocol
conforms to Session Initiation Protocol In preferred embodiments,
said second protocol is an application layer protocol.
[0033] Preferably, said second protocol conforms to an Internet
mail transfer protocol.
[0034] Thus, SIP messages can be addressed to an existing address
identifier, for example and e-mail address identifier constructed
in accordance with Simple Mail Transfer Protocol (SMTP), and
translated to a corresponding SIP address identifier for
transmission to a SIP user agent server regardless of whether the
SIP address identifier is known to the user. Thus, the present
invention enables messages to be readily diverted from a SIP
defined destination URL address identifier to a corresponding SMTP
defined destination URL address identifier for the same user or end
system. In this way users may send SIP messages to SMTP address
identifiers using the SMTP network protocol and infrastructure and
SMTP messages to SIP address identifiers using the SIP network
protocol and infrastructure.
[0035] According to another aspect of the invention there is
provided a software program for implementing said method.
[0036] According to a further aspect of the invention there is
provided a system for processing control messages constructed in
accordance with a first communications protocol for use in a
communications network, each control message including a first
address identifier having a format defined by said first protocol;
said system comprising: [0037] a processor for processing said
control message to derive a second address identifier from said
first identifier, said second identifier having a format defined by
a second communications protocol; and, [0038] a message constructor
for re-formatting said control message for transmission, in
accordance with said second protocol, to a network device
associated with said second address identifier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The invention will now be described with reference to the
accompanying drawings in which:
[0040] FIG. 1a is a schematic representation of a typical SIP
message signalling sequence in a network comprising a SIP re-direct
server;
[0041] FIG. 1b is a schematic representation of a typical SIP
message signalling sequence in a network comprising a SIP proxy
server;
[0042] FIG. 2 is a block diagram of a SIP user agent;
[0043] FIG. 3 is a block diagram of a SIP user agent graphical user
interface;
[0044] FIG. 4 is a schematic representation of a communications
network comprising a plurality of SIP enabled network domains;
and,
[0045] FIG. 5 is a flow diagram of a method implemented in the
communications network of FIG. 4.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0046] With reference to the drawings, typical signalling sequences
are shown in FIGS. 1a and 1b between two user agents 100 and 102
connected over a communications network using a SIP redirect server
106 (FIG. 1a), and a SIP proxy server 108 (FIG. 1b). In both
arrangements a SIP location server 110 is connected to the
respective SIP network server for address resolution.
[0047] In FIG. 1a, user agent 100 sends a SIP Invite message 112 to
user agent 102. The Invite message is received at and processed by
the re-direct server 106 to determine the network location of user
agent 102. The re-direct server sends a location query 114 to the
location server 110. The location server determines the current
network location of user agent 102 and sends this information to
the re-direct server in a message 116 for transmission to the user
agent 100 in a message 118. User agent 100 then sends an Invite
message 120 to user agent 102, either directly or via other SIP
re-direct or proxy servers, which then responds by sending an
acceptance message 122 to the user agent 100. User agent 100
completes the session or call set up procedure by sending an
acknowledgement 124. Once the session has been set up information
can be exchanged between the respective user agents.
[0048] In FIG. 1b, user agent. 100 sends a SIP Invite message 126
to user agent 102 as before but instead of being processed by a
re-direct server the message is processed by the network proxy
server 108. The proxy server sends a location query 128 to the
location server 110. The location server determines the current
network location of the user agent 102 and sends this information
back to the proxy server in a message 130. The proxy server then
relays the Invite message to the user agent 102 by means of a
message 132 which is processed by the user agent 102. A call
acceptance message 134 is then sent back to the proxy server which
relays a corresponding message 136 to the user agent 100. The user
agent 100 then sends an acknowledgement message 138 to the proxy
server which similarly relays a corresponding message 140 to the
user agent 102.
[0049] With reference now to FIG. 2, a typical SIP user agent 200
comprises a front end system in the form of a graphical user
interface (GUI) 202, a SIP client program 204, a SIP server program
206, a media module 208, a network interface 210 a SIP address
cache 212, a SIP URL address generator 214 and a SIP message
processor 216.
[0050] A typical SIP GUI is shown in FIG. 3. The GUI 202 comprises
a plurality of buttons 302 to 310 each of which represents a
different SIP request method. Button 302 represents the SIP
"INVITE" request for inviting a callee to a SIP session, button 304
represents the "OPTIONS" request for discovering the capabilities
of the receiving terminal, button 306 represents the "BYE" request
for terminating a call or a call request, button 308 represents the
"CANCEL" request for terminating incomplete call requests and
button 310 represents the "REGISTER" request method for registering
the current location of the user with a respective domain location
database 110. The respective request methods are invoked by a user
clicking the respective button, by mouse controlled cursor click or
otherwise. The GUI further comprises a text box 314 labelled "To:
SIP URL" for user input, by keyboard entry or address book entry
selection for example, of the SIP address identifier of an intended
callee, that is to say the SIP destination message header field
"To"; a text box 316 labelled "To: e-mail URL" for user input of
the e-mail address identifier of the intended callee; and, a text
box 318 labelled "Title" for displaying title information to
identify the session. A further text box 320 is provided for the
input of other SIP message text including for example other SIP
header types and text comprising the SIP message body. Text may be
input into any one of the text boxes 314, 316, 318, 320 using known
text processing means, for example, keyboard entry, selection from
pull down menus or cut and paste text processing applications.
[0051] The SIP message constructor is configured to process data
entered into any one of the boxes 314, 316, 320, 320 and construct
a SIP message including the relevant request type for transmission
to an appropriate SIP network server. For example, the message
constructor copies the text entered in the text box 314 to the SIP
message header type "To:" in the SIP message being constructed.
Other header types are determined by the message constructor such
as "Content-type:" and "Content length:" for example.
[0052] The user agent client program is configured to initiate a
SIP session or "call" and the user agent server program is
configured to respond to a call. In this regard the user agent
client program implements the SIP request methods Invite, Options,
Bye, Cancel and Register, and the user agent server implements the
methods Invite, Bye, Cancel and Ack methods. Messages are passed
from the user agent client to the network interface 210 for
transmission to the intended callee associated with the destination
SIP URL address. SIP messages are received at the destination end
by the network interface and are processing by the user agent
server. The media module 208 provides the necessary API's for
sending system calls to appropriate media applications for
processing different media types once a SIP session has been
established.
[0053] When a user wishes to initiate a SIP session, the user
interacts with the GUI 202 to construct a SIP Invite message
including a destination SIP or e-mail address. Once all the
necessary data has been input to the GUI, including the SIP header
types and message body, the message processor constructs an
appropriate SIP message for transmission to the callee. In the
event that the callee's SIP URL address is unknown to the user, the
user inputs the callee's SMTP e-mail address in the text box 316.
The e-mail address is then sent to the SIP URL generator 214.
[0054] The SIP URL generator 214 comprises a software program for
generating a SIP URL address identifier from a respective SMTP
e-mail address identifier for a respective user.
[0055] The SIP URL generator is configured to process the e-mail
address identifier, in accordance with a set of pre-determined
rules, to generate a corresponding SIP URL address identifier for
the callee. In one arrangement, the e-mail address is processed by
the SIP URL generator which adds a prefix address component to the
existing e-mail address components "user@host" etc. The prefix
address component identifies the communications protocol that the
new URL is to be used with. In this embodiment "sip" is added as a
prefix. A suffix address component is also added to identify a SIP
domain name authority the newly generated SIP URL address
identifier is to be identified with. In one example the SIP URL
generator is configured to process the SMTP e-mail address
"alan.oneill@bt.com" to derive the SIP URL address identifier
"sip:alan.oneill@bt.com.sipit.com", that is to say, to add the
protocol prefix "sip" and the domain suffix "sipit.com" to the
existing SMTP readable e-mail address "alan.oneill@bt.com". Thus,
the SIP URL generator is configured to generate SIP URL address
identifiers by processing a respective address identifier
constructed in accordance with the Internet e-mail communications
protocol SMTP. In another example the SIP URL generator is
configured to process the same SMTP e-mail address identifier to
derive the SIP URL address identifier
"sip:alan.oneill@bt.com.uk.sipit.com", that is to say a
geographical identifier "uk" is additionally added to the SMTP
e-mail address identifier. The additional geographic identifier may
assist scalability of the name space and hence network routing
efficiency of the resulting SIP message, for example.
[0056] Referring now to FIG. 4, a plurality of network domains 400,
402 and 404 are each connected to the Internet 406 by means of a
respective SIP network server 408, 410 and 412. In the network of
FIG. 4 the SIP network servers are configured for use both as SIP
proxy and SIP re-direct servers. The SIP network servers provide
access to and from the respective domains. Each network domain
comprises a plurality of SIP user agents 200(a-g). SIP user agents
200a, 200b and 200c are connected to the network server 408 in the
domain 400, SIP user agents 200d, and 200e are connected to the
network server 410 in the domain 402, and SIP user agents 200f and
200g are connected to the network server 412 in the domain 404.
Each SIP network server is connected to a respective location
server 110 for SIP address resolution and an associated SIP to SMTP
e-mail gateway 414. Each SMTP e-mail gateway is connected to a
respective SMTP Mail Transfer Agent (MTA) 416 for relaying SMTP
e-mail messages to respective destination SMTP MTA's over transport
layer TCP connections.
[0057] Each SIP to SMTP e-mail gateway 414 comprises an SMTP e-mail
address generator 418 and a message processor 420 which comprises
an SMTP user agent. The e-mail address generator comprises software
for generating an SMTP address identifier from a SIP URL address
identifier. In this regard the e-mail address generator is
configured in a similar but reverse manner to the address generator
214. The e-mail address generator is configured to process the SIP
URL destination address identifier of an out going SIP message to
derive a corresponding SMTP e-mail address identifier. The e-mail
address generator processes the SIP URL address in accordance with
the same pre-determined set of rules as the SIP address generator
214, but processes these rules in reverse order with respect to the
address generator 214. For instance, in one embodiment a SIP
message arriving at the SIP to SMTP e-mail gateway 414 is parsed to
determine the destination SIP URL. The SIP URL is then passed to
the SIP to e-mail address generator 418. The remaining part of the
SIP message is re-formatted by the message processor 420 into SMTP
format suitable for transmission as an SMTP e-mail message.
[0058] In one embodiment the address generator 418 is programmed in
accordance with the above set of rules, that is to say to remove
the protocol identifier prefix "sip" from the SIP URL address and
to remove the sip domain suffix component "sipit.com". The address
generator sends the re-formatted SMTP address identifier to the
message processor where the newly derived SMTP address is added to
the re-formatted message as the destination SMTP address for that
message. The message processor adds the newly generated SMTP
address to the SMTP "To:" header field of a respective SMTP
message. For example, the address generator 418 is programmed to
derive the SMTP e-mail address identifier alan.oneill@bt.com from
SIP URL "sip:alan.oneill@bt.com .sipit.com".
[0059] The message processor 420 constructs an appropriate SMTP
message for transmission to the newly generated SMTP address
according to the content of the respective SIP control message. For
example, the SIP message payload, for example the SDP message
component of the SIP message, is added as text to the respective
SMTP message body for transmission to the respective destination
SMTP address. In the example described with reference to FIG. 3,
the SDP text shown in box 320 is processed and added as text to the
SMPT message payload by the message processor 420.
[0060] With reference now to the flow diagram of FIG. 5, a user
initiates a SIP session in step 500 by interaction with the GUI 202
of a SIP user agent 200. A data entry for each of the required data
types is input by the user including a destination SIP address in
box 314 or, in the absence of a known SIP URL for the intended
recipient, an SMTP e-mail address that is known to be allocated to
the recipient in box 316. Data relating to the SIP message is
processed into SIP format by the SIP message processor 216 and is
then submitted to the user agent client 204 by the user selecting
the Invite button 302 by mouse click or other data input command.
The user agent client determines in step 502 whether a SIP URL
address has been provided or an SMTP e-mail address. If a SIP URL
has been provided processing proceeds to step 508. However, if an
SMTP e-mail address identifier has been provided the user agent
client sends the e-mail address to the address generator 214 for
processing to a respective SIP URL address identifier in step 504.
A respective SIP URL is generated in accordance with the above
described method. In step 506 the newly derived SIP URL address is
added to the SIP destination header type "To:" following the INVITE
request type of the SIP message.
[0061] The SIP message is transmitted to the appropriate local SIP
network server 408,410 or 412 in step 508 to be relayed or
re-directed to a network server associated with the destination SIP
URL address. The network server that receives the SIP message
queries its associated location database 110 in step 510, using DNS
or other address resolution means, to determine the network server
the SIP message should be transmitted to. In step 512 a network
server having authority for the domain for the destination SIP URL
determines whether the destination SIP URL address is a valid
network address, that is to say, whether the SIP URL address has
been allocated by the domain authority to a SIP user. The SIP URL
destination address is a valid network address if it can be
resolved by a location database using DNS or other resolution means
to a respective numerical IP address, for example. In this respect
address resolution may involve querying other location databases
associated with other network SIP servers or SIP domains in a
similar way that DNS resolves numerical IP addresses. In step 514,
if the destination SIP URL address is valid, that is to say it has
been allocated to a respective user and can be resolved, the
location server returns the IP address of the next SIP server that
is configured to relay or re-direct the message or if appropriate
the IP address of the end system currently associated with the
destination SIP URL. The SIP message is sent to the next SIP
network server or destination end system in step 516. If the SIP
URL is invalid, that is to say it has not been allocated by the
appropriate domain authority for use in the network, an appropriate
SIP network server transmits the SIP message to an associated SIP
to SMTP e-mail gateway in step 516. The destination SIP URL may be
invalid for instance because it was automatically generated from a
known e-mail address identifier in step 504 and no corresponding
SIP address exists. Under these circumstances the message processor
420 re-formats the SIP message to an SMTP message for communication
over the Internet 406 in accordance with SMTP in step 518. In step
520 the destination. SIP URL address is processed by the address
generator 418 in step 520 to derive the SMTP e-mail address
encapsulated within the SIP URL address. Additional information and
data is added to the re-formatted SMTP e-mail message in step 522
including, for example the text: [0062] "You were called by SIP
user <sender's SIP URL and associated data> at <time,
date> with message <SIP message body content (SDP)> but
you were not found in the SIP registration system. You can register
at <http hyperlink> where you can download a SIP client." or,
[0063] "You were called by SIP user <sender's SIP URL and
associated data> at <time, date> with message <SIP
message body content (SDP)> but you were not found in the SIP
registration system. You can register using the attached http form
<http registration form with mailto: URI address>. A SIP
client <SIP client executable code> is attached."
[0064] The SMTP message is sent to an associated mail transfer
agent 416 in step 524 for transmission to the e-mail address
derived in step 520 using the SMTP network protocol. In step 526
the sender is informed by the SIP server that the destination SIP
URL was not valid and that the message was instead re-formatted
according to SMTP and sent to the SMTP e-mail address derived in
step 520.
[0065] It will be seen that the other embodiments of the present
invention could be readily implemented by the skilled person, for
instance instead of the SIP message being diverted to a SIP to
e-mail gateway in the event that the destination SIP URL address is
invalid, a SIP message could be readily diverted to a SIP to e-mail
gateway if the user or the end system associated with the user was
unavailable or unwilling to receive SIP messages at the time of
message transmission. In one embodiment, the respective SIP server
selects an appropriate message from an associated message library
(not shown) for inclusion with the original SIP message in step
522. The message library includes a respective delivery failure
message for each SIP message delivery failure mode, including for
example, destination SIP user agent unavailable, user unavailable,
network connection failure, user unwilling to join SIP session or
user unwilling to join designated sessions, user will be available
at <time, date>, etc.
[0066] It will also be seen that in other embodiments the SIP to
e-mail gateway 414 could be readily implemented in other network
devices such as a respective network SIP server or a SIP user
agent.
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